Method and apparatus for a distributive wide area network for a land mobile transmission trunked communication system

ABSTRACT

A land mobile transmission trunked communication system is provided with a unique switching protocol arrangement among repeaters that are networked to one or more external communication networks. The land mobile transmission trunked communication system includes a plurality of transceivers for transmitting and receiving transmission trunked radio communications over one or more radio channels. The transceivers communicate with a selected one of a plurality of repeaters to establish transmission trunked radio communications on a preassigned radio channel. The unique switching protocol arangement includes a switch that is operably connected to each repeater and selectively communicates information signals between a repeater and an external communication network. A bus system is operably connected to each repeater and to the switch for communicating control signals among all of the repeaters and the switch. The control signals include an indication for each repeater which is controlled by that repeater and by the switch as to free channel availability. Because the mechanism for controlling indications of free channel availability is operationally separate from the switch, the repeaters continue to provide transmission trunked communications to the transceivers in the event of a failure of the switch.

This is a continuation, of application Ser. No. 07/903,050, filed Jun.23, 1992, now abandoned, which is a continuation of U.S. Pat. No.5,159,701, issued Oct. 27, 1992 from Ser. No. 07/716,757, which was acontinuation of an original application Ser. No. 07/332,675, filed Mar.31, 1989, now abandoned.

TECHNICAL FIELD

This invention pertains to land mobile radio communication systems. Inparticular, the present invention pertains to a method and apparatus fordistributively interconnecting a plurality of land mobile transmissiontrunked communication systems into a wide area network. The inventionincludes switching and signaling protocols especially adapted forcommunication of control signals in the subaudio band an expandedfeature set of radio communications capabilities.

BACKGROUND ART

Mobile radio communication systems provide for two way radiocommunications between a central control station and a fleet of cars,trucks, or other vehicles. Typical users of mobile radio communicationsystems include, for example, police departments, fire departments, taxiservices and delivery services. Present mobile radio communicationsystems can be configured to provide for radio communications betweenthe control station and all vehicles in a fleet, between the controlstation and selected vehicles in the fleet, or between differentindividual vehicles or groups of vehicles within a fleet.

Conventional mobile radio communication systems are typically organizedwith a number of vehicles and a control station assigned to a singlecommon channel for a given coverage zone. A user assigned to the commonchannel must wait until no one else is transmitting on that channelbefore sending a message, because only one transmission at a time can beprocessed by a single channel. Even when a transmission is addressed toonly one user in a conventional system (and therefor not heard by otherusers), the other users in the system must wait until that transmissionis completed before they can use the system to communicate.

Mobile radio communication systems using transmission trunking are animprovement over conventional mobile radio communication systems in thattrunked systems enable two or more users to communicate on the system atthe same time. For instance, the dispatch console in a transmissiontrunked communication system can be communicating with one of thevehicles in the fleet; while, at the same time, two other vehicles inthe fleet can be using the same trunked system to communicate with eachother. Transmission trunked communication systems group a number ofchannels for the same coverage zone together into a single radiocommunication system, with each channel accessible to each user in thesystem. Because each user will only need to communicate over the trunkedsystem part of the time, and because it is unlikely that all users willneed to communicate at precisely the same time, the number of channelsassigned to a trunked system group can always be less than the number ofusers allocated to that trunked system group.

The United States Federal Communications Commission (FCC) has assigned600 channels in the 800 MHz band for trunked land mobile use. Eachchannel is comprised of a pair of assigned frequencies, a mobiletransmit frequency and a repeater transmit frequency. Mobile transmitfrequencies are 806-821 MHz, with the repeater transmit frequenciesexactly 45 MHz above the corresponding mobile transmit frequency, or851-866 MHz. Channel spacing is 25 KHz, with the maximum alloweddeviation between channels being +/-5 KHz. In September 1987, the FCCalso allocated 399 channels in the 900MHz band for trunked land mobileuse. Mobile transmit frequencies are 896-901 MHz, with the repeatertransmit frequencies exactly 39MHz above the corresponding mobiletransmit frequency, or 935-940 MHz. Channel spacing is 12.5 KHz, withthe maximum allowed deviation between channels being +/-2.5 KHz.

In transmission trunked communication systems, a signaling protocol isused to send and receive control signals among users on each channel Inthe trunked system and a switching protocol is used to establish whichchannels those users will be communicating over. The preferredconventional transmission trunked communication system uses a signalingprotocol that transmits the control signals In the subaudio bandsimultaneously with the transmission of voice or data informationsignals. Signaling protocols that can communicate control signals withinthe constraints of the subaudio band are preferred, because use of thesubaudio band precludes the need for using a dedicated channel fortransmitting the control signals (thereby reducing the number ofavailable channels In the trunked system for voice and datacommunications). A switching protocol is used by the trunked system toautomatically find and engage an open channel when a user initiates atransmission. To maximize the trunking capabilities of such a system,the switching protocol must efficiently allocate channels in the trunkedsystem and avoid channels that are already in use at the time thetransmission is initiated. For further explanation of the preferredconventional transmission trunked communication systems, reference ismade to the description of the operation of the ClearChannel LTR® systemcontained in the manual entitled "E. F. Johnson ClearChannel LTRApplication Note", Part No. 009-0001-020 (Rev. 5, Oct. 1988), availablefrom E. F. Johnson Company, Waseta, Minn., a copy of which is attachedas Appendix A and is fully Incorporated by reference herein.

Transmission trunked communication systems have proven to be aneconomical and effective means for establishing voice and datacommunications between a dispatch console or control station and a fleetof mobile vehicles in a given coverage zone. However, the capability ofsuch trunked systems to provide radio communications over a wide areaserviced by a plurality of preferably adjacent coverage zones has beenlimited because of the problems involved in linking multiple coveragezones and because of the limitations of the switching and signalingprotocols of present transmission trunked communication systems.

Present transmission trunked communication systems of the type describedabove are generally unable to transfer voice/data communication betweencoverage zones, because the repeaters in such systems are interconnectedonly by a single time slot status bus. As a result, the only method ofinterconnecting repeaters in different coverage areas is to use anexternal network, i.e. routing the communication as a long-distancetelephone call from a repeater interconnect or interface to a telephoneexchange and then back through a second repeater interconnect to theremote repeater location. These channels are then "hung" to lock thechannels in for the duration of the call. In addition to the increasedexpense and inconvenience of such an external network, the use of arepeater interconnect prevents usage of the channels in each trunkedsystem over which the communication is occurring for the entire periodof the communication.

Even in those instances where inter-coverage zone communications aremade through an external network, such communications are forindividuals calls, not fleet calls, and are limited to a few preselectedusers on each system. It would be desirable to provide unique ID numbersfor each user on a wide area network to allow for direct entry of theunique ID to establish private communication between users on thenetwork, as well as fleet calls between groups of users on the network.Unfortunately, it is impossible to accommodate unique ID numbers in thepreferred present transmission trunked communication system because thenumber of digital bits required to represent such unique ID numbersexceeds the maximum number of bits that the trunked systems cancommunicate via the established signaling protocol. The signalingprotocol of the preferred transmission trunked communication system isalso limited in the number of channels that may be grouped together pertrunked system. For example, the signaling protocol of the LTR® trunkedsystem is limited to 20 channels per system and uses a look-up table totranslate the channel information transmitted by the signaling protocolinto the actual frequency pair assigned to that channel.

Another problem with the conventional switching and signaling protocolsis that such protocols are unable to allow for the implementation of anextended feature set of radio communication capabilities on thepreferred conventional transmission trunked communication systems. Forexample, present trunked systems are generally unable to establishpriority access for users in a given coverage zone. Present trunkedsystems are also unable to interrogate and reprogram or otherwise modifythe operation of mobiles without having the mobile transceiver unitphysically brought to a service facility to be reprogrammed. A mobiletraveling from one coverage zone to another coverage zone, for instance,needs to be reprogrammed for a different set of groups over whichcommunications will be received. Such reprogramming cannot be done "onthe fly" in present systems, and mobiles are therefor not able totransit coverage zones at will.

One approach to a wide area network for communications systems iscellular telephone networks. In cellular telephone networks, a largenumber of overlapping coverage zones (cells) are used to providecoverage over an entire area. The primary difficulties that must beovercome by cellular networks relate to the handoff of communicationswhen a mobile transceiver moves from cell to cell during a transmission.This type of approach is unnecessary for transmission trunkedcommunications systems because the coverage zones of trunked systems aremuch larger. In addition, because transmissions on a transmissiontrunked communication system are trunked and are relatively short, thereis no need to handoff a mobile transceiver from one coverage zone tomother during a transmission. Although automatic handoff of radiocommunications is well developed in cellular radiotelephone systems,such an automatic handoff occurs within a coordinated single systemunder the direction of a central processing system, not between separatecoverage zones utilizing distributed processing techniques.Consequently, the body of knowledge regarding such handoff techniques isnot particularly applicable when coordination between two or moretrunked systems is minimal and the trunked systems are to bedistributively interconnected.

Another approach to a wide area network for transmission trunkedcommunication systems uses a separate control channel for communicatingcontrol signals and simulcasts the same message on the same frequenciesfor different coverage zones. This approach requires an extensivecentralized processing capability to monitor and assign channels forcommunications extending beyond a single coverage zone. Still anotherapproach to a wide area network for transmission trunked communicationsystems uses a high speed mode to communicate extended control signalswith the mobile transceivers in a coverage zone. Although the use of ahigh speed mode allows for large amounts of control information to becommunicated with the mobile, the use of different transmission speedsmay cause signal degradation and possibly missed communications becauseof the required switching between high speed mode and normalcommunications with the mobile transceiver.

The underlying problem with previous approaches to establishing a widearea network for a transmission trunked communication system is that thenetworks are centralized and require significant amounts of controlinformation to be both communicated between the repeaters and the mobile(either by a dedicated control channel or by the use of a high speedmode) and be processed by a central processing unit that coordinates allof this information about each user in the entire network. Each of thesesystems results in increased overhead, both in terms of the hardwarerequired to operate the trunked systems and the network itself, and interms of the amount of control signals and other information that iscommunicated between the repeater and the mobile transceivers. Moreover,the use of a centralized approach to the wide area network significantlydecreases the fault tolerance capabilities of the network and of thetransmission trunked communication systems themselves. The reliance on apowerful central processing capability to perform the network operationsleave users open to the possibility of loss of radio communicationservice in the event that the central processing unit fails.

Although present transmission trunked communication systems have provento be an economical and effective means for establishing voice and datacommunications between a control station and a fleet of mobile vehiclesin a given coverage zone, it would be advantageous to provide a methodand apparatus for distributively interconnecting a plurality of landmobile transmission trunked communication systems into a wide areanetwork that included switching and signaling protocols especiallyadapted for communication of control signals in the subaudio band and anexpanded feature set of radio communications capabilities.

SUMMARY OF THE INVENTION

In accordance with the present invention, a method and apparatus fordistributively interconnecting a plurality of land mobile transmissiontrunked communication systems into a wide area network is provided. Theinvention includes a plurality of distributive radio network terminal(RNT) switch means and a unique signaling protocol and a switchingprotocol especially adapted for communication of control signals in thesubaudio band for interconnecting a plurality of transmission trunkedcommunications systems into a wide area network. The switching andsignaling protocols hereof provide an expanded feature set of radiocommunications capabilities.

Each of the transmission trunked communication systems of the presentinvention includes a plurality of transceiver means for transmitting andreceiving transmission trunked radio communications over one or morechannels and a plurality of repeater means for establishing transmissiontrunked radio communication between the repeater means and one or moreof the transceiver means. The transmission trunked radio communicationsare made up of an information signal (voice or data information) and acontrol signal (control information transmitted pursuant to a signalingprotocol) and are communicated between the transceiver means and therepeater means with the control signals transmitted simultaneously inthe subaudio range of the same channel over which the informationsignals are being transmitted.

The distributive RNT switch means and the trunking architecture of thesignaling protocol and switching protocol of the present invention arespecifically designed to provide trunked transmission radiocommunications to a large fleet of users. The features and operationalparameters of both the RNT switch means and the transmission trunkedcommunication systems are directed at users who are dependent on fast,reliable, fleet-based dispatching for their everyday operations. Thetrunking architecture utilizes a signaling protocol and switchingprotocol that are designed for high density traffic and fast accesstime, and which allow for an expanded feature set of communicationoptions. The system is spectrum efficient, using all licensed channelsfor voice/data communication and transmission trunking to eliminatewasted air time between message exchanges.

The present invention is designed to provide the greatest benefits thelargest percentage of time for the primary users of such a transmissiontrunked communication system. These users include the governmentservices market, both emergency and nonemergency, the utility market,the public transportation market, the large industrial complex market,and the SMR (specialized mobile radio) market. The requirements forthese markets are similar in many ways, but because the public safetyrequirements are more stringent, the trunking architecture is designedusing the public safety requirements as the standard.

The distributively interconnected transmission trunked communicationsystems of the present invention meet these requirements by providingcentralized full-featured dispatching with the ability to view theentire operation of the network utilizing a central control console thatcan monitor and participate in multiple calls simultaneously. Theinvention provides unique identification of users on all transmissions,including fleet calls, and provides for a method of priority access toenable emergency and non-emergency users to share the same system. Thesignaling protocol includes a dual word system key encryption of alltransmissions on the network for increased security. The invention alsoallows for dynamic reconfiguration of the transceivers means byover-the-air commands using special control signals, including automaticor manual registration of mobile transceivers in a new system, homechannel backup, and the capability to disable mobile transceivers. As awide area network, the present invention provides the capability of fullduplex or half-duplex communications with individual users or groups ofusers over a plurality of coverage zones. Because of the distributiveand modular nature of the RNT switch means of the present invention, itis possible to integrate the transmission trunked communication systemsof the present invention with conventional channel systems or with thepresent LTR trunked systems. Each RNT switch means includes a systemmanagement module that allows the user to selectively configure thetransmission trunked communication system for that particular user'sneeds, as well as monitor the activity on the trunked system. Otherfeatures and advantages of the present invention will be described inthe detailed description of the preferred embodiment set forth below.

Accordingly, it is an objective of the present invention to provide amethod and apparatus for distributively interconnecting a plurality ofland mobile transmission trunked communication systems into a wide areanetwork.

It is a further objective of the present invention to provide a uniquesignaling protocol and a switching protocol especially adapted forcommunication of control signals in the subaudio band forinterconnecting the transmission trunked communications systems into awide area network that also provides for an expanded feature set ofradio communications capabilities.

It is an additional objective of the present invention to provide uniqueidentification of users on all transmissions in a transmission trunkedcommunication system.

It is a still further objective of the present invention to provide amethod and system of priority access for users in a transmission trunkedcommunication system.

It is a still further objective of the present invention to provide amethod and system for dynamic reconfiguration of mobile transceivers ina transmission trunked communication system, automatic or manualregistration of mobile transceivers in a new system, and home channelbackup.

These and other objectives of the present invention will become apparentwith reference to the drawings, the detailed description of thepreferred embodiment and the appended claims.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is an overall block diagram of the preferred embodiment of amultiple radio network terminal (RNT) switch means implementing the widearea network mobile radio communication system of the present invention.

FIG. 2 is a pictorial representation of a multiple site conventionaltransmission trunked land mobile communication system.

FIG. 3 is a pictorial representation of the RNT switch means of thepresent invention.

FIG. 4 is a block diagram of the control message used in a conventionaltransmission trunked land mobile communication system.

FIG. 5 is a block diagram of the time slot bus used to connect repeatersin a conventional transmission trunked land mobile communication system.

FIG. 6 is a block diagram of the control message in accordance with thepresent invention.

FIG. 7 is a block diagram of the high speed repeater data bus inaccordance with the present invention.

FIGS. 8a-8c are block diagrams showing the three alternate methods ofestablishing priority access in accordance with the present invention.

FIG. 9 is a block diagram showing various interconnections of themodules for the RNT switch means in accordance with the presentinvention.

FIG. 10 is a block diagram showing various methods of interconnectingthe RNT switch means with the repeaters and the dispatch consoles withina coverage zone.

FIG. 11 is a block diagram showing various methods of interconnectingmultiple RNT switch means to provide a wide area network of multiplecoverage zones.

FIG. 12 is a block diagram showing the various modules for the RNTswitch means.

FIGS. 13a-13c are block diagrams of the data, control and voice busstructures of the RNT switch means.

FIG. 14 is a flow diagram broadly depicting the operation of a mobiletransceiver within a distributive wide area network transmission trunkedcommunication system in accordance with the present invention.

FIG. 15 shows the relationship of FIG. 15a-15c

FIG. 15a-15c are flow diagrams depicting in greater detail step 309 ofFIG. 14.

FIG. 16 shows the relationship of FIG. 16a-16b

FIG. 16a-16b are flow diagrams depicting in greater detail step 306 ofFIG. 14.

FIG. 17 shows the relationship of FIG. 17a-17b

FIG. 17a-17b is a flow diagram depicting in greater detail steps 308312of FIG. 14.

FIGS. 18a-18c are flow diagrams of three dynamic reconfigurationfeatures.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to FIG. 1, the preferred embodiment of the method andapparatus for distributively interconnecting a plurality of land mobiletransmission trunked communication systems into a wide area network willbe described. The invention includes a plurality of distributive radionetwork terminal (RNT) switch means 10 that utilize a unique signalingprotocol and a switching protocol especially adapted for communicationof control signals in the subaudio band. There is one RNT switch means10 for each transmission trunked communication system. Each transmissiontrunked communication system includes a plurality of transceiver means12 for transmitting and receiving transmission trunked radiocommunications over one or more channels and a plurality of repeatermeans 14 for establishing transmission trunked radio communicationbetween the repeater means 14 and one or more of the mobile transceivermeans 12. The transmission trunked radio communications comprises aninformation signal and a control signal using transmission trunking,with the control signals transmitted simultaneously in the subaudiorange on the same channel over which the information signals aretransmitted. The RNT switch means 10 are used for selectivelyinterconnecting two or more of the repeater means 14 in each trunkedsystem, as well as providing the link between trunked systems in a widearea network.

The RNT switch means 10 may also be connected to a dispatch consolemeans 16 for monitoring the users at the transceivers means 12 anddispatching calls and other communications. Alternatively, a remotelylocated control station means 18 may also be used to perform thedispatching function on the system. The control station means 18 mayinclude a selective call console and communicates with the repeatermeans 14 by way of radio communication to link to the RNT switch means10, rather than via a direct or hard-wired connection with the RNTswitch means 10. In addition, the RNT switch means 10 may be connectedwith the telephone central office 20 or an external communicationnetwork 22 (e.g, a satellite communication system or a private PBXsystem) to allow users on the system to make and receive communicationsor calls outside of the network.

Two or more of the RNT switch means 10 may be interconnected by a nodeswitch means 30 that operates as a high speed voice grade communicationpath between two RNT switch means 10. The node switch means 30 may beany type of matrix switching equipment or PABX that is capable ofhandling directed voice switching. The RNT switch means 10 may also beinterconnected to a registration means 32 for maintaining a database ofregistration information that can be communicated among the switch meansas a mobile transceiver moves from coverage zone to coverage zone asdescribed hereinafter. Finally, one or more of the RNT switch means 10may be connected to a monitoring means 34 for monitoring activity on thenetwork and performing record keeping, billing and other accountinginformation functions. The activities of the node switch means 30, theregistration means 32 and the monitoring means 34 may be containedwithin a single computer linked to each of the RNT switch means 10, ormay be distributed among several processors linked to one or more of theRNT switch means 10, depending upon the type of configuration and thefunctions that are required of a particular user's network.

The general operation of an independent transmission trunkedcommunication system associated with each RNT switch means 10 will nowbe described. Control signaling between the repeater means 14 associatedwith an RNT switch means 10 and the transceiver means 12 is done withsubaudio control signals on each channel designated as a "home channel".Each mobile transceiver means 12 in the trunked system is assigned to ahome channel that it monitors when the transceiver is not involved in acall. The transceiver means 12 may be either a mobile transceiverlocated in a car or a handheld transceiver. (The terms mobile,transceiver and mobile transceiver as used hereinafter refer to any suchtransceiver means 12). The transceiver means 12 receives control signalinstructions over the home channel to either stay on the home channeland open its audio to receive a call, or to change to a differentchannel and open its audio to receive a call. If the transceiver means12 was sent to another channel to receive a call, it will return to itshome channel as soon as the call is completed.

When a transceiver means 12 wants to initiate a call, all the operatorhas to do is depress the push-to-talk (PTT) button and hold it. If thehome channel assigned to the mobile transceiver means 12 is available,the transmitter for the transceiver means 12 will transmit a controlsignal on the home channel frequency telling the repeater means 14 thata call is being setup on that channel. At that point, the transceivermeans 12 turns its transmitter off and waits for a return message fromthe repeater means 14. If the repeater means 14 is not busy, therepeater means 14 will broadcast a handshake message that will bereceived by all mobile transceiver means 12 assigned to the same homechannel. The operator of the initiating transceiver means 12 will hearan audible proceed tone and its transmitter will be enabled to proceedwith the call. For this type of fleet calling, all other transceivermeans 12 with the correct fleet identification will remain on thechannel and open their squelch to receive the call. All transceivermeans 12 that did not have the proper fleet identification would remainmuted, but the logic unit of the transceiver means 12 would receive andstore the control signal indicating that their home channel was now busyand that they would get a free channel assignment. As a result, if atransceiver means 12 not involved in the call described above now wantedto initiate a call, it would know where a free channel was so that itwould not have to look for a free channel in the trunked system.

If the home channel for a transceiver means 12 was busy when a call wasinitiated, the initial data transmission would be made on the freechannel that It had stored in memory. The repeater means 14 receivingthe call would notify the repeater means 14 for the home channelassigned to the transceiver means 12 Initiating the call that a call wasbeing setup on the free channel for a fleet assigned to the home channelrepeater means 14. The home channel repeater means 14 would then addthis information to the control signal being sent out over the homechannel, and would also change the free channel assignment to anotherfree channel. The transceiver means 12 that had a proper fleetassignment would receive the control signal sent out over the homechannel that a call was being setup for their fleet on the directedchannel and would switch to that channel and open their squelch toreceive the call. All other transceiver means 12 that did not have theproper fleet assignment would store the free channel information andwould continue to monitor the home channel.

To understand how the method and apparatus for a mobile transmissiontrunked communication system wide area network of the present inventionoperates, it is helpful to divide the discussion of the preferredembodiment into a discussion of the signaling and switching protocolused by the invention and a discussion of the architecture andorganization of both the wide area network and the individualtransmission trunked communication systems associated with each RNTswitch means 10. The overall philosophy behind both the protocols andthe architectures that will be explained is a distributive approach tonetworking, as compared to the centralized approach currently applied towide area networks for transmission trunked communication systems. Thisdistributive philosophy reduces the overhead involved in managing thenetwork and the trunked systems, while at the same time increases thereliability of the network and each trunked system by eliminatingreliance on critical components and providing for built-in backupfeatures to insure that communications over the network and the trunkedsystems are maintained.

Signaling Protocol Architecture

The architecture for the signaling protocol of the present invention isan enhanced and expanded version of the LTR® signaling protocol that wasfirst introduced into the United States market in 1980 and has sincebecome the de facto transmission trunking standard. Familiarity with theLTR system, including the LTR signaling protocol, the LTR repeaters andthe various LTR compatible mobile transceivers can be obtained from areview of the previously incorporated reference attached hereto asAppendix A and is presumed for the discussion that follows.

Referring now to FIGS. 2 and 3, the differences between a conventionalmultiple site LTR repeater configuration and a transmission trunkedcommunication system of the present invention will be explained. In theLTR configuration shown in FIG. 2, the mobile transceiver means 12(Mobiles A. B and C) and the control station means 18 of System 1 cannotcommunicate with the mobile transceiver means 12 (Mobiles D and E) ofSystem 2. The repeater means 14 use a time slot bus 40 that indicateswhich channels are free and which channels are busy in the System. Thetime slot bus 40 allows the Mobiles in either System 1 or System 2 onlyto communicate with each other within their respective system byidentifying a free channel and communicating together on the repeatermeans 14 associated with that channel. The time slot bus 40, combinedwith the LTR control message format described below, limit thecommunication between repeaters in the LTR system to a method forassigning free channels in a group of channels (repeaters) that comprisea given trunked system. There is no provision to communicate informationsignals (voice/data communication) among repeaters in a trunked system,let alone communicate information signals between repeaters located indifferent trunked systems.

In the transmission trunked communication system shown in FIG. 3, eachof the repeater means 14 is interconnected with a high speed data bus 42that provides for an improved switching protocol that allows data wordsto be communicated among the repeater means 14. The control messageformat of the signaling protocol of the present invention is alsosignificantly changed to incorporate a unique identification for eachmobile transceiver means 12 and to implement the priority access scheme,as well as other enhancements to the feature set of radio communicationcapabilities. In addition, each of the repeater means 14 is alsoconnected by a network bus means 44 with the RNT switch means 10 for therespective trunked system. As described in greater detail hereinafter,the network bus means 44 allows information signals to be communicatedamong repeaters in a system, as well as allowing both control andinformation signals to be communicated with another RNT switch means 10,or with an external communication network, i.e., a telephone exchange.

LTR Switching and Signaling Protocol

Referring now to FIG. 4, the control message formats 100 and 102 for theLTR signaling protocol is shown. In the LTR system shown in FIG. 2,system control is accomplished by sending control messages 100 and 102shown in FIG. 4 between the repeater means 14 and the mobiletransceivers 12 and control stations 18. Control message signalingoccupies the subaudio frequencies below 150 Hz of a channel and occurseven when voice or data information is present on the channel. Controlmessages 100 are continuously transmitted to the repeater means 14 bythe calling mobile transceiver means 12 while a conversation is inprogress. The repeater means 14 also continuously transmits controlmessages 102 to the called mobile transceiver means 12, as well as toall other mobile transceiver means 12 monitoring that channel. Thespecific information in the control message 100 and 102 depends onwhether it is repeater or mobile transmitted. The width of each bit inthe control message is 3.36 msec (a data rate of approximately 300 baud)and a complete control message for the LTR signaling protocol istransmitted in approximately 135 msecs.

The data fields in the control messages 100 and 102 include:

Sync 104--The first two bits are used to initialize the receive datacircuitry of the mobile transceiver. The other bits are used to detectthe arrival of the control message 100 and provide bit synchronization.

Area 106--With mobile transmitted control messages 100, this is the areaprogrammed in the mobile; with repeater transmitted control messages 102messages, it is the bit programmed by the repeater programming switch.If the area transmitted in a control message does not agree with theprogrammed area, the call attempt will be unsuccessful. This bit isusually coded "0" unless there are two LTR systems close enough toInterfere with each other. In that case, it would then be coded "0" inone trunked system and "1" in the other trunked system.

Go-To 108--In a control message 100 from the mobile, this field containsthe number of the repeater (1-20) to which the message is beingtransmitted. These bits must be the same as the number assigned to therepeater or the message is appearing on the wrong channel because ofintermodulation and will be ignored. In control message 102 from therepeater to the mobile, this field contains the repeater number. Incontrol messages to mobiles being trunked out to other repeaters, thisfield contains the repeater number (channel) to which those mobilesshould switch to receive a message. If the repeater is not busy, acontrol message 102 is transmitted every 10 seconds to keep the mobilesupdated. The Go-To 108 field then contains the number of the repeater.When the mobile push-to-talk switch is released, the transmitter remainson for a short time and sends a turn-off code in this field. This codeis retransmitted by the repeater and it tells the receiving mobiles tosquelch and resume monitoring the home channel. This prevents a "squelchtail" (noise burst) when the transmitting mobile unkeys.

Home Repeater 110--In a mobile-to-repeater control message 100, thisfield contains the home repeater number of the mobile being called. Thisnumber is always the programmed home repeater number In the selectedsystem of the mobile making the call. In a repeater-to-mobile controlmessage 102, this field contains the same repeater number received inthe data message from the mobile. If the repeater is not busy, ittransmits its own number in this field.

ID Code 112--In a mobile-to-repeater control message 100, this fieldcontains the ID code (1-250) of the fleet or sub-fleet being called. Ina repeater-to-mobile control message 102, this is the ID code of thefleet or sub-fleet being called on that channel. If other mobilesassigned to that channel have bean trunked to other repeaters,additional messages are transmitted containing the ID code of thesemobiles. In this case, the ID code information is from the repeater timeslot bus 40.

Free Channel 114--In a mobile-to-repeater control message 100, thisfield contains a pass code. In a repeater-to-mobile control message 102,this field contains the number of a repeater that is not busy and isavailable for service. The free repeater is chosen in a random manner asdescribed in the next section. This information tells mobiles assignedto that repeater which repeater to use to make a call. If a repeater isnot busy, it transmits its number in this field. If all repeaters arebusy, a "0" is transmitted in this field.

Error Check Bits 116--These seven bits are used as a checksum to checkfor data errors In a data message. If an error is detected, the messageis rejected.

Referring now to FIG. 5, the LTR switching protocol will be described.In a LTR transmission trunked communication system, a single-line serialbus interconnects the logic units of all the repeaters in the trunkedsystem. The serial bus is time-divided to act as a time slot bus 120.One repeater in the system is programmed to generate a synchronizationpulse that is used by all other repeaters in the system to determinetheir time slot 122 on the time slot bus 120. Time slots 1-20 are usedby the respective repeaters and time slot 21 is used by the IDValidator. The time slot 122 used by each repeater is determined by therepeater number assigned to that repeater when the programming switch isset. For example, Repeater 1 uses time slot 1, repeater 5 uses time slot5, and so on. The data rate on the time slot bus 120 is 18,750 baud.

During its time slot 122, each repeater plates information on the timeslot bus 120 indicating the status of that repeater. The time slot 122consists of a first word 124 and a second word 126. If a repeater is notbusy, only the start bits 128 appear in the time slot 122. If a repeateris busy, information appears in its time slot 122 identifying the homerepeater 130 and ID code 132 of the mobile being called on that channel.If a repeater number is unassigned, nothing appears in the time slot122. Each repeater monitors all the time slots and if that repeater'snumber is detected in another time slot, the repeater beginstransmitting an additional control message using the signaling protocoldescribed above. This message tells a mobile to go to another channel toreceive a message. This additional message is transmitted for as long asthe mobile is transmitting on the other channel.

The free repeater indicated In the Free Channel 114 field of controlmessage 102 as shown in FIG. 4 is determined by continuously monitoringinformation in the twenty time slots 122. The free repeater numberchanges as these slots are monitored. If a time slot 122 has only startbits 128 indicating an idle repeater, that is the current free repeater.If information in a time slot 122 indicates no repeater or a busyrepeater, the free repeater number does not change. For example, assumea five repeater system with repeaters assigned numbers 1, 5, 9, 13, and17. If repeaters 5 and 13 are busy, the free repeater changes as followsas the twenty time slots are monitored: 1 1 1 1 1 1 1 1 9 9 9 9 9 9 9 917 17 17 17. The free repeater transmitted in the Free Channel 114 fieldof control message 102 is the free repeater detected at the instant themessage is composed.

Although the present combination of LTR signaling protocol for controlmessages and switching protocol for determining free channels is anefficient means of signaling mobile and assigning free channels in asingle transmission trunked communication system, these same protocolshave prevented the use of the LTR system as a wide area network capableof providing transmission trunked radio service over a number ofcoverage zones. In addition to the lack of voice/data communicationamong repeaters in a trunked system and the inability to communicateeither control or information signals between repeaters located inmultiple systems, there is no capability to provide for the uniqueidentification necessary to properly interconnect multiple trunkedsystems together into a wide area network.

Signaling and Switching Protocol of the Present Invention

The signaling and switching protocols of the present invention allow theadvantages of the LTR signaling protocol to be retained, while allowingmultiple systems of repeaters to be grouped together in a wide area,transmission trunked radio communication system. In addition, anexpanded feature set is provided that supports features beyond thosefeatures currently available on LTR transmission trunked communicationsystems. The result is a mobile transmission trunked communicationsystem wide area network that does not need a dedicated control channelbecause the control signals are transmitted subaudibly, simultaneouslywith the information signals, that provides a fast access time throughthe system (approximately 0.5 secs) that will not increase as the numberof channels in a system are increased, that provides continuous controlsignaling to enable mobiles just brought into service or coming out of afade to begin monitoring a call automatically (this is imperative inpublic safety systems where the risk of loss of communication in anemergency situation is critical), that has a signaling protocol that isfrequency transparent and can be used on different frequency bands, thatprovides unique identification numbers for each mobile on the entiresystem, and that encodes the trunked transmissions to preventunauthorized reception.

Referring now to FIG. 6, the control message format for the signalingprotocol of the present invention is shown. The data fields in thecontrol messages 150 and 152 include:

Sync 154--The first two bits are used to initialize the receive datacircuitry of the mobile transceiver. The other bits are used to detectthe arrival of the control message 150 or 152 and provide bitsynchronization.

Reserved 156--With mobile transmitted control messages 150, the Reserved156 bit is always a "0". With repeater transmitted control messages 152,Reserved bit 156 is used to indicate that the control message 152 willnot be decoded by the repeater and sent back out. In other words, theReserved bit 156 indicates that the control message is from the repeaterand it is used on critical messages sent from the RNT switch means 10,for example, commands relating to dynamic reprogramming such as disablemobile, reprogram mobile, etc.

Go-To 158--In a control message 150 from the mobile, this field containsthe FCC channel number of the repeater to which the message is beingtransmitted. These bits must be the same as the number assigned to therepeater or the message is appearing on the wrong channel because ofintermodulation and will be ignored. Unlike the 5 bit Go-To 108 used inthe LTR signaling protocol, Go-To 158 does not require that the mobilebe equipped with a predetermined look-up table in order to determine theproper frequency to transmit and receive. The channel number containedin Go-To 158 can be used to directly calculate the transmit and receivefrequencies, thereby simplifying the logic in the mobile transceiver. Incontrol message 152 from the repeater to the mobile using the channel,this field contains the FCC channel number. In control messages tomobiles being trunked out to other repeaters, this field contains theFCC channel number to which those mobiles should switch to receive amessage. If the repeater is not busy, a control message 152 istransmitted every 10 seconds to keep the mobiles updated. The Go-To 158field then contains the FCC channel number of the repeater. When themobile push-to-talk switch is released, the transmitter remains on for ashort time and sends a turn-off code in this field. This code isretransmitted by the repeater and it tells the receiving mobiles tosquelch and resume monitoring the home channel. This prevents a "squelchtail" (noise burst) when the transmitting mobile unkeys.

Home Repeater 160--In a mobile-to-repeater control message 150, thisfield contains the home repeater number of the mobile being called(1-30). This number is the programmed home repeater number in theselected system of the mobile making the call and may form a part of thehome/group ID of the particular fleet or sub-fleet using the trunkedsystem. In a repeater-to-mobile control message 152, this field containsthe same repeater number received in the control message from themobile. If the repeater is not busy, it transmits its own number in thisfield.

Group 162--In a mobile-to-repeater control message 160, this fieldcontains the Group ID codes (1-254) of the fleet or subfleet beingcalled. In a repeater-to-mobile control message 152, this is the GroupID code of the fleet or sub-fleet being called on that channel. Aportion of the Group ID codes from 225-254 are reserved for specialfunctions as described in greater detail hereinafter. It should be notedthat the mobile units can be programmed with a different Group ID encodeand decode, depending upon how the particular trunked system is to beconfigured.

Free Channel 164--In a repeater-to-mobile control message 152, thisfield contains the FCC channel number of a repeater that is not busy andis available for service. This information tells mobiles assigned tothat repeater which repeater to use to make a call. If a repeater is notbusy, it transmits its own channel number in this field. If allrepeaters are busy, a "0" is transmitted in this field.

Unique 166--In both the mobile-to-repeater control message 150 andrepeater-to-mobile control message 152, Unique 166 generally containsthe unique ID code of the transmitting mobile or of the transmittingdispatch console. The 13 bits of Unique ID 166 provide up to 8,192unique identification codes with 0, 8, 164-8191 being reserved forspecial functions. In special function calls, Unique 166 containsspecial function data, such as control information for dynamicreconfiguration.

Priority 168--In the mobile-to-repeater control message 150, this fieldindicates the 5 level APCO (Association of Public CommunicationsOfficers) standard priority level assigned to the mobile transmittingthe control message. The mobile priority information is also used by theRNT switch to monitor that priority of all of the currently active callsin case the trunked system is full and a dispatch console has requestedthe RNT switch to force a user off the trunked system to free up achannel for an emergency call. In the repeater-to-mobile control message152, this field indicates thepriority level currently on the trunkedsystem. If in the last control message 152 that a mobile has received anaccess priority level for Priority 168 that is higher than the prioritylevel assigned to the mobile, then the mobile will not attempt to usethe trunked system.

The various methods of using the priority access scheme of the presentinvention are best understood by reference to the state diagrams shownin FIGS. 8a-8c. In the first case, FIG. 8a, the priority access systemis set-up with no channels in the trunked system reserved for emergencyor priority use. In this case at State 200, if all channels are busy,Priority 168 is set to "1" and only those mobiles with a priority of "1"will attempt to access the trunked system. If one channel frees up atState 202, Priority 168 remains at a "1". If two or more channels freeup at State 204, then Priority is set to "5" and all mobiles may nowattempt to access the system. A timed cascading sequence is entered onceState 202 is reached such that after each 0.5 seconds of elapsed timewithout a change in a channel freeing up or becoming busy, the level ofpriority in Priority 168 is deceased by one to "2" at State 206, "3" atState 208, "4" at State 210, and finally to "5" at State 212 two secondsafter State 202 was originally entered. In FIG. 8a, a priority schemefor a trunked system having one channel reserved and two effectivelevels of priority is shown. At either State 220 or 222, Priority 168 is"1" to Insure that there will be at least one channel open if there is achannel free in the trunked system. At State 224, Priority 168 is set to"5" to allow all users to access the trunked system. In FIG. 8c, acombination of reserved and non-reserved priority schemes is shown wherethere is one reserved channel and five levels of priority. At States230, 232 and 234, Priority 168 is "1" to insure that at least onechannel will remain free. At State 236, if three or more channels arefree, Priority 168 is set to "5" to allow all users to access thetrunked system. At State 234, a timed cascading sequence similar to thatof State 202 is entered that starts the decrease in priority levelsthrough States 238, 240, 242 and 244, when Priority 168 is set to "5"after two seconds of no new activity on the trunked system.

Chk 170--These eight bits are used as a checksum to check for dataerrors in a data message. If an error is detected, the message isrejected. The first seven bits of Chk 170 are derived from a truncatedBCH (127,120) encoding scheme performed on a selected portion of thecontrol message 150 and 152, as described below. The eighth check bit isa simple parity bit based on the number of bits in the selected portionof the control message 150 and 152 and the 7 BCH check bits. It shouldbe noted that although a known BCH encoding scheme is used, any othertype of encoding scheme known in the art could be used as well. In thepreferred checksum technique, the eight-bit Chk 170 checksum is usedonly to detect the presence of errors in the control message and not tocorrect errors. The eight-bit checksum enables 100% detection of allone-, two-, and three-bit errors and also all odd errors of five bits orgreater. In addition, approximately 99.3% of all even errors of fourbits or greater are detected.

Unlike the prior LTR signaling protocol, Chk 170 is also used as part ofan encryption coding scheme to increase the security of the signalingprotocol. A two word system key is provided to each repeater means 14and transceiver means 12 on the trunked system. This two word key isused to encode and decode each of the transmissions on the trunkedsystem. In the preferred embodiment, prior to computing the checksum, aselected number of bits from the control message are bit-operated on bythe first word of the two word key. The preferred bit-operations toencode a bit stream are well known and may include transposition,exclusive or, shifting, or any other equivalent technique. After thisstep, the entire control message, except Sync 154, is used to computethe eight-bit checksum. With the checksum completed, a secondbit-operation is performed on the completed checksum with the secondword of the system key to encode it prior to placing the 8-bit checksumin Chk 170. This dual encoding scheme significantly increases thedifficulties associated with decoding the transmission because thereceiver of the control signal is never sure whether the transmissionwas a good transmission without bit errors unless the second word of thesystem key is used to decode the checksum information.

RSVD 172 and Stat 174-152. RSVD 172 is reserved for future expansion andStar 174 is defined to return the current status of the mobile.

Referring now to FIG. 7, the high speed repeater data bus 42 for therepeater means 14 of the present invention will be described. Theprincipal behind the switching protocol for the repeater data bus 42 isto provides a method for a fixed number of repeater means 14 tocommunicate quickly and efficiently over a common data bus withdistributed control and variable time frame, while still maintainingsynchronization on the bus. The switching protocol on the repeater databus 42 is arranged into time slots or messages 180. Each message 180 ismade up of a fixed number of words 182 that are in turn made up of afixed number of bits. An entire group of messages for a particulartrunked system is a frame. All of the repeater means 14 monitor therepeater data bus 42 constantly, but transmit on the repeater data bus42 only during their respective timeslot. In the preferred embodiment,the maximum period for a timeslot is the length of one message 180(approximately 2.4 msecs), with each message 180 comprised of 6 words182, each word consisting of a start bit, 8 data bits, a sync bit and astop bit.

Unlike the switching protocol of the present LTR trunked system, theswitching protocol of the present invention does not rely on a fixednumber of messages in a frame to determine the position of the timeslots in that frame. As explained below, the length of a time slot maybe effectively shortened if the repeater means 14 designated to transmitduring that time interval is missing from the trunked system by skippingthe message 180 associated with the missing repeater. The ability toskip messages 180 in the format of the frames for the signaling protocolof the present invention minimizes the time period of the frame fortrunked systems having less than the maximum number of 30 repeaters. Italso provides the capability for communicating control signalinformation among the repeaters without increasing the time period ofthe frame beyond the point where performance of the entire trunkedsystem is degraded.

The first word 182 of each message 180 is uniquely identified as thefirst word by the sync bit 184. When the sync bit 184 is a "1", the word182 is recognized by all of the repeaters means 14 on the repeater databus 42 as the beginning of a new message 180. For all other words 182 ina message 180, the sync bit 184 is set to "0". The contents of the firstword 182 are From 186, the FCC channel number of the repeater meanstransmitting this message 180. When the sync bit 184 is received by eachrepeater on the repeater data bus 42, the repeater updates the time slotcount of the repeater number to the repeater number in From 186. Whenall of the words 182 of the message 180 have been received, the timeslot count is incremented to look for the repeater number of the nextrepeater. Thus, if all of the repeaters in a five repeater trunkedsystem are present, the protocol of the repeater data bus 42 would looklike that shown in the first frame shown in FIG. 7. If a repeater is notpresent for a time slot, or if the repeater does not communicate acomplete message 180, all of the other repeaters on the trunked systemwait for a delay period of a little more than one word and thenincrement the time slot count to the next repeater. In this way, thetime slots associated with missing or defective repeaters can besequenced through much faster than the normal time period. When one ormore of the repeaters are missing, the protocol of the repeater data bus42 would look like the second or third frame shown in FIG. 7.

The second word 182 of the switching protocol is To 188--the channelnumber of the repeater to whom the following four Data Words 190 aredirected. The remaining four words 182 of the switching protocol areData Words 190 consisting of R 156, GoTo 158, Group 162, and Unique 166from the switching protocol described above. The ability to transmit thesame information being sent out by one repeater to another repeater inthe trunked system allows the trunked system to more efficiently monitorand account for the mobile transceiver in the trunked system.

Also, unlike the Switching protocol of the present LTR trunked system,the switching protocol of the present invention is not dependent upon aspecified repeater in the trunked system to send out the sync word ofthe protocol format. Because each repeater on the repeater data bus 42is distributively responsible for establishing synchronization with theother repeaters, a repeater may be added to or removed from the trunkedsystem without affecting the operation of the trunked system and withoutthe need to reprogram the repeaters on the trunked system. Moreover, thetrunked system is not dependent upon any single repeater to establishthe synchronization for the repeater data bus 42. If one repeater was tofall, the rest of the trunked system would continue to operate and,because of the backup home channel feature, the users would notice onlya possible small degradation in service because of one fewer trunkedchannels on the trunked system.

It will be apparent that the signaling and switching protocols of thepresent invention will allow a variety of features and options to beimplemented to establish an expanded feature set for the mobilecommunication system wide area network of the present invention,including: variable operation, traffic logging, diagnostics, groupvalidation, selective unit disable, dynamic reconfiguration, priorityaccess, redundant repeater control, home channel backup, dynamic channelassignment, and automatic or manual registration.

The home channel backup feature of the present invention assigns abackup channel for each transceiver means 12 on the trunked system.Generally, for each trunked system, one non-home channel will beassigned as the backup channel for all of the home channels on thetrunked system. In the event that a transceiver means 12 does not detectany communication on its home channel for a predefined period of time(in the preferred embodiment, approximately 1 minute), the mobileswitches to the preassigned backup channel. As the home channel repeatermeans normally is broadcasting an update control message at least every10 seconds, if the mobile has not received any communications for thelast six update periods it will assume that its home channel has goneoff the air and will switch to the backup channel. After switching tothe backup channel, if the mobile transceiver does not detect anycommunication on the backup channel for a predefined time period, themobile will presume that it has gone out of the coverage zone of thetrunked system and, if it has been programmed to do so, will attempt toautomatically register on any of the other available trunked systems inthe wide area network that the mobile is a user on. If, after switchingto the backup channel, the mobile does detect communication, the mobilewill use the backup channel as its home channel until such time as thebackup channel transmits a control message containing the original homechannel of the mobile in the Go-To 158 field. To implement adistributive approach to the home channel backup, the designated backupchannel retransmits the home channel update information of all of thehome channels for the trunked system at selected intervals on the backupchannel. Thus, if the home channel returns to the air after a period ofinactivity, it will begin transmitting update information that willperiodically be repeated on the backup channel, thereby insuring thateach of the mobiles for that home channel will return to their originalhome channel.

Dynamic reconfiguration of the mobile transceivers in any of the trunkedsystems of the wide area network of the present invention isaccomplished without the need for an exchange of overhead informationbetween the repeater and the mobile by using a select portion of theGroup ID's in Group 162 and the unique identification number of themobile or a data field in Unique 166 to transmit the necessary commandsin the control message 152 sent from the repeater to the mobile. In thepreferred embodiment, the Group ID's between 230 and 254 are reservedfor these special communication functions. The information sent andreceived in the Unique 152 field will vary depending upon the particulardynamic reconfiguration function being performed.

It will be understood that the operation of dynamic reconfiguration onthe trunked system requires compatible software programming in both theRNT switch and the mobile, along with reprogrammable memory in themobile for those functions that will change or reprogram initial ordefault values that have been stored in the mobile. For example, a giventransceiver means 12 is originally programmed with a specific set ofauthorized groups for the trunked system it will be operating in. Thesegroups a may be stored in a table in memory (i.e., an EEPROM) in themobile logic unit. If the mobile were to travel out of the coverage zoneassociated with the trunked system it is assigned to and into anothercoverage zone, the mobile could also have stored in its memoryregistration channels associated with adjacent coverage zones that itwould allow the mobile to contact those trunked systems. When it isdetermined that the mobile has left the original zone and entered a newcoverage zone, the mobile would contact the trunked system in the newcoverage zone and request automatic registration in that zone. The newRNT switch means 10 for that zone would contact the home RNT switchmeans 10 through the registration means 32 to verify that the mobile wasallowed to register in the new coverage zone and inform the home RNTswitch means 10 that the mobile had left its coverage zone. Once themobile is registered in the new coverage zone, the new RNT switch means10 might reprogram the group that the mobile was associated with mightreprogram,

The signaling protocol for any of the function includes the same basicsteps of: (1) transmitting a NOP special code with the Unique ID of themobile being reconfigured (this step is repeated four times on thechannel of the mobile being reconfigured to insure that if the mobile isin the coverage zone it will receive the command); (2) transmitting oneor more of the special Group ID's for the particular command or functionbeing performed and transmitting the appropriate data for that functionin the Unique 166 field; (3) transmitting a DONUT (do nothing) specialcode with the Unique ID of the mobile being reconfigured to indicatethat the particular command or function is complete; (4) waiting for acommand acknowledgement (if the command was accepted) or a commandno-acknowledgement (if the command was rejected) special Group ID to betransmitted by the mobile in response to the particular command orfunction; and (5) waiting for a timeout condition if no commandacknowledgement or no-acknowledgement is received. FIGS. 18a-18c aresample flow diagrams of three types of dynamic reconfiguration, aSelective Unit Disable, a Reassign Group ID, and a Reassign Select Data.

The RNT Switch Means

The Radio Network Terminal (RNT) switch means 10 of the presentinvention connects several forms of communication systems together in anetwork system that allows communication between users of the networksystem and also allows a plurality of network systems to be linkedtogether into a single wide area network The RNT switch means 10provides the interface to standard communication consoles (dispatchconsoles 16 or control stations 18) for central dispatching and control.The RNT switch means 10, in conjunction with the dispatch consoles 16 orcontrol stations 18, provides the mechanism to utilize the expandedfeature set of the signaling protocol previously described, includingUnit Interrogate, Unit Status, Priority, Dynamic Reassignment, SelectiveUnit Disable, etc.

Configuration of the RNT Switch Means

Referring now to FIG. 9, the various forms of communication systems thatare interfaced with the RNT switch means 10 are shown. The RNT switchmeans 10 is capable of controlling up to 30 channels of radiocommunications. The channels can be a combination of conventionalchannel repeaters 24, LTR repeaters 26 or the repeater means 14 of thepresent invention. The maximum number of each of these types ofrepeaters is 30 for the conventional channel repeaters 24, 20 for theLTR repeaters 26, and 30 for the repeater means 14 of the presentinvention. The node switch means 30 allows communication with anotherRNT switch means 10.

The RNT switch means 10 connects the various communication paths amongthese elements and gives priority access to the proper modules. Systemtrunking during calls is preserved through the RNT switch means 10unless fixed by full-duplex or the use of hangtime. Access time forcalls to and from any one of the trunked systems is approximately 0.5seconds, excluding signaling time for external devices such as ToneRemote detection time and the passing of DTMF information. The RNTswitch means 10 automatically routes outgoing telephone calls to thetelephone central office 20 on the least cost line and produces atraffic accounting record of calls made by Group and/or Unique ID. Therecord may be accessed by the monitoring means 34 and includes: calltime, call duration, telephone number dialed, and if a transceiver means12 terminated or originated the call. In the preferred embodiment, theserecords are preserved in non-volatile disk memory.

Wide area coverage between multiple RNT switch means 10 is directed byDTMF entries from either the requesting transceiver means 12 or thetelephone control office means 20 or the control stations means 18. Widearea coverage on a group basis within a given RNT switch means isperformed by a crosspatch of the dispatch console means 16 to thedesired repeater means 14. Wide are coverage on either a group orindividual basis outside the RNT switch means 10 is determined by therequesting mobile transceiver means 12 and is established by the nodeswitch means 30.

Referring now to FIGS. 10 and 11, various methods for interconnectingthe elements associated with the RNT switch means 10 are shown. In FIG.10, the RNT switch means 10 is shown as interconnecting by RFcommunication with conventional channel repeaters 24 (either VHF orUHF), by microwave link with an LTR repeater 26, and by microwave,leased line, or direct connection with the repeater means 14 of thepresent invention. The RNT switch means 10 may be connected with thedispatch console means 16 by RF communication, by microwave link, bydirect connection or by leased line through a telephone interconnect. InFIG. 11, the various methods of linking multiple RNT switch means 10 ina wide area network are shown. The RNT switch means 10 may be connectedwith the node switch means 30 via microwave link, leased lines or bydirect connection. The registration means 32 may also be connected withthe RNT switch means by each of these methods. Again, the RNT switchmeans 10 may be connected to the repeater means 14 by any variety ofmethods, depending upon whether the repeater means 14 is physicallylocated proximate or distant to the RNT switch means 10.

Architecture of the RNT Switch Means

Referring now to FIG. 12, the internal architecture of the RNT switchmeans 10 will be described. The main interfaces to the RNT switch means10 include the Channel Interface to the various channels, the interfacewith Dispatch Consoles 16, the interface with the Public SwitchedTelephone Network 20, the interface to other RNT's via the Node Switchmeans 30, and the interface to the System Manager. The RNT switch means10 is constructed of different modules that interface from the RNTswitch means 10 to external devices.

The modules as shown in FIG. 12 and described in the following sectionsare: the Channel Interface Module (CIM), connecting the RNT switch means10 to the either a LTR repeater or to the repeater means 14 of thepresent invention; the Conventional Channel Module (CCM), connecting theRNT switch means 10 to a Conventional Channel; the Dispatch InterfaceModule (DIM), connecting the RNT switch means 10 to the DispatchConsoles 16; the Telephone Interface Module (TIM), connecting the RNTswitch means 10 to the PSTN 20 or PABX 22; the System Network Module(SNM), connecting the RNT switch means 10 to other SNM's, and, via thenode switch means 30, to other RNT switch means 20; the Voice ToneModule (VTM), providing voice and tone messages to the RNT switch means10; the Network Interface Module (NIM), connecting the RNT switch means10 to the SMM; and; the Switch Manager Module (SMM), providing setup andmonitoring capabilities for the RNT switch means 10.

The System Manager Module controls the portion of the RNT switch mean 10that connects various communication paths by programming various optionson the different connections. Programing is done on a computer equippedwith a color monitor and sufficient serial ports for communication withthe necessary system elements and an option printer. The system managerfunctions are protected against access by a minimum of one securitylevel. In the preferred embodiment, the SMM is an 80286 based computer,including a keyboard, color monitor; 640K RAM, 1 floppy disk, and a 40Megabyte hard disk. The functions performed by the SMM include: monitortraffic and produces a usage record; determine channel usage and amountof time all channels in a site are busy in time periods of 6, 10, 15, 30or 60 minutes; receive notification as soon as a channel or systemelement failure is detected; program hangtime, initiated on an mobilechannel from the switch, to hold a connection on the Trunked System;program a Dispatch Console 16 (equipped with connection control) withthe ability to participate in a call; program a Dispatch Console 16 forfull duplex communication (the dispatch console 16 informs the systemwhen full duplex communication takes place); program a Dispatch Console16 for "All Call" transmissions and priority levels (A request for "AllCall" transmission acquires all channels in a trunked system fortransmission from the dispatch console); program a Dispatch Console withpriority levels associated with the Group IDs; initiate ID Validationthat determines if a Group or Unique ID is allowed to use the system forvoice communication or any operation. and maintain a list of which IDsare enabled or mobile units disabled for operation by the switch;performs dynamic reconfiguration of an mobile unit in the Multi-NetTrunked System; perform least cost routing for outgoing telephone calls.

The Network Interface Module (NIM) interfaces the Switch ManagementModule (SMM) to the internal communication of the RNT switch means 10.The NIM buffers data communication via a full duplex RS-232 channel onthe Intra-terminal Data Bus (IDB) to the System Management Bus (SMB).The NIM is also a buffer between the Channel Status Bus (CSB) to theSystem Status Bus (SSB). This data is a "snap shot" of the channelactivity sent once every two seconds on a RS-232 channel in onedirection only, from the NIM to the SMM. The NIM provides the MasterClock and Master Sync for the signaling control of the pulse codemodulation (PCM) voice busses. The Master Clock and Master Sync for thePCM busses are redundant in the NIM. A detection circuit monitors thetwo different sets and if master dock A is off frequency, B isactivated. If both A and B are off frequency, an alarm is sent to theSMM and the NIM removes both sets from distribution in the RNT switch.The RNT switch is allowed a Master and Slave NIM, enabled or disabledfrom operation on the data communication path. The master tells theslave when both its clocks are off frequency and the slave clock isdistributed, if the slave clocks are on frequency.

The Channel Interface Module (CIM) connects the RNT switch means 10 tothe repeater means 14 and to LTR Repeaters 26. Each repeater means 14has a CIM that monitors and controls the repeater through a signalingprotocol. The CIM controls a LTR repeater means 14 through the Multi-NetLogic Module (MLM). A MLM is the logic drawer in the repeater thatinterfaces the CIM in the RNT with the receiver and transmitter in therepeater. The MLM is connected to the CIM by 4-wire 600 ohm balancedaudio. The MLM is controlled by blank and burst mode, 1200 baud, AudioFrequency Shift Keying (AFSK) data or by digital RS-232 data for bothtransmit and receive data. The CIM passes information to and from theMLM that controls the repeater and its operation.

The Conventional Channel Module (CCM) connects the RNT switch means 10to a conventional repeater 24. Each conventional repeater 24 has a CCMthat controls the repeater through logic signaling. The CCM controls aconventional repeater through the Conventional Repeater Module (CRM). ACRM is the logic drawer in the repeater that interfaces the CCM in theRNT with the transmitter and receiver in the repeater. The CRM isconnected to the CCM by 4-wire 600 ohm balanced audio. The CRM iscontrolled by blank and burst mode, 1200 baud, Audio Frequency ShiftKeying (AFSK) data for both transmit and receive data. The CRM connectsto the repeater via 4-wire 600 ohm balanced or unbalanced audio. The CCMreflects the activity of the repeater and acts as a gateway fortransmissions between the RNT switch and the conventional repeater, thusallowing the conventional repeater to look like an LTR repeater or therepeater means of the present invention for a given site, home, andgroup.

The Dispatch Interface Module (DIM) uses one of three methods ofinterface the RNT switch to the dispatch equipment, Direct Connection,Tone Remote, and Digital Data. A DIM with direct connection isassociated with only one group code and uses a form of Type II E & Mlead input similar to the mobile PTT. A DIM with tone remote connectiondecodes guard tone for the PTT Indication and decodes DTMF to selectfrom one of ten group codes. A control sequence uses the DTMF to placethe DIM in scan mode or to stop and use a specific group code. The toneremote feature requires the use of an add on personality card. The mostversatile DIM has a digital-data connection that requires a separatefull duplex 9600 baud, RS-232 channel. The separate data path isrequired because the intelligent dispatch console can monitor anddisplay the information of the system. The information exchanged betweenthe DIM and an intelligent dispatch console contains what the DIMreceives and transmits. The DIM connects the 4-wire 600 ohm balancedaudio with the Pulse Code Modulation (PCM) data paths and communicatesto other modules via the Intra-terminal Data Bus (IDB). The DIM alsomonitors the Channel Interface Module (CIM) Channel Status Bus (CSB) todetermine if a CIM 1s active with a DIM group: Some of the functionsperformed by the DIM include: unique ID display: status display: uniqueID calling: emergency display: emergency answer: site select calling;interrogate--static and dynamic.

The Trunk Interface Module (TIM) connects the RNT switch to thetelephone lines and handles telephone line protocols. The TIM logic unitis microprocessor controlled and communications to the Switch ManagementModule (SMM) via the intra-terminal data communications. A RNT may havemultiple TIMs with varying styles of telephone lines attached, forexample, connection to Central Office, or connection to PABX system. Thetelephone line audio is processed to interface with the Pulse CodeModulation (PCM) voice path. The basic TIM operation functions are:Signaling, Call Supervision and Intra-terminal Communications.

The System Network Module (SNM) is the interface that allows Unique IDcalling from mobile units and multiple RNT switches to be connected in atotal wide area network. The SNM uses a 4-wire 600 ohm balanced audio onthe interface and connects audio to the PCM data paths. The SNM alsouses a Type II E&M lead connection set for connection initiation andsupervision. The SNM communicates with other modules via theIntra-terminal Data Bus (IDB) and monitors the Channel Status Bus (CSB)for the group set up to use the SNM. The RNT switch may be one terminalin a multiple terminal system created by connecting the RNT switch viathe SNM, through a 4-wire E&M lead interface, to a system switching nodeor Private Automatic Branch Exchange (PABX). The SNM can dial pulse orDTMF the desired site, another SNM interface in the same RNT switch orin a different RNT switch. SNM's pass information on the interfacerelative to the type of call desired and connection status of the enddevice using Audio Frequency Shift Keying (AFSK) in a blank and burstmode. This form of data passing allows a standard 4-wire interfaceconnection and does not require a specialized system switching node.

The Voice Tone Module (VTM) provides tone and voice messages to modulesthat indicates call progress to the users. The VTM contains 8-fixedslots of digitized PCM audio messages stored in PROM that are 4-secondsin length and repeat continuously on the VTM PCM bus of the RNT switch.The start of the message is indicated in the transmission so modules canpresent the audio message to the user from the beginning of a message.There may be up to four VTMs within a system, depending upon themessages required.

The various bus means that interconnect the modules of the RNT switchmeans 10 are shown in FIGS. 13a-13c. Together, these busses comprise thenetwork bus 44 that links the various modules in the RNT switch means 10to one another and to the repeater means 14. FIG. 13a shows theinterrelationship of the various modules and the data busses. TheMessage Accounting Bus (MAB) is a 9600 baud bus with a sync-escapeprotocol. The MAB passes information of the system call status once asecond, telephone accounting data, and error records. The Channelinterface Bus (CIB) is a 1200 baud sync-escape protocol bus that passessystem channel control and status to and from the CIM. The ChannelStatus Bus (CSB) is a 19200 baud sync-escape protocol bus that passeschannel status from channel modules to other system modules. TheDispatch Interface Bus (DIB) is a 1200 baud syncescape protocol bus thatpasses DIM control and status to and from the Dispatch Consoles. TheDispatch Tone Protocol (DTP) passes industry standard tone remotepush-to-talk tone and DTMF for DIM control and status to and from thedispatch consoles. The Intra-Terminal Data Bus (IDB) is a 19200 baudsync:escape protocol bus that modules communicate on to pass controlinformation to each other. The System Network Bus (SNB) is a 1200 baudsync-escape protocol bus that passes control and status from one SNM toanother. The System Management Bus (SMB) is a 9600 baud syncescapeprotocol bus that passes information from the SMM to and from the othermodules via the NIM. The System Status Bus (SSB) is a 9600 baudsync-escape protocol bus that passes the CSB data to the SMM or externalperipheral equipment once every 2 seconds via the NIM. The RegistrationBus (RGB) is a 9600 baud syncescape protocol bus that passes the mobileunit registration information to and from the registration system.

Referring now to FIG. 13b, the control busses used to control the flowof data and voice information in the RNT switch means 10 are shown. TheIDB Idle/Collision line is a three level line that indicates if the lineis idle, busy or collision occurred for the IDB communication process.The CSB Idle/Collision line is a three level line that indicates if theline is idle, busy or collision occurred from the CSB communicationprocess.

In FIG. 13c, the voice busses that pass information signals (eithervoice/data) The VTM Bus is a 2.048 MHz Pulse Code Modulated (PCM) buscontaining 32 slots of tones or voice the modules use to indicate callprogress to an end user by means of audio information. The Tx PCM bus isa 2.048 MHz Pulse Code Modulated (PCM) bus containing 32 slots. Audioreceived from the mobile channel is transmitted on these slots by thechannel modules and received by the other system modules. The Rx PCM busis a 2.048 MHz Pulse Code Modulated (PCM) bus containing 32 slots. Audiois transmitted from the other system modules to these slots and receivedby the channel modules to be transmitted on the mobile channel. TheMaster Sync provides the synchronization signal for the PCM buscommunication to begin the frame of 32 PCM slots. The Master Clockprovides the 2.048 MHz clocking signal for the PCM busses.

For a more detailed technical description of the circuitry associatedwith the RNT switch means 10, as well as a more derailed description ofthe operation and setup of the RNT switch means 10, reference is made tothe reference is made to the description of the operation of the E. F.Johnson Multi-Net™ system contained in the manual entitled "Multi-Net™Radio Network Terminal Service Manual", Part No. 001-3039-001 (Rev. 1,Mar. 1989), which will be available from E. F. Johnson Company, Waseca,Minn., a copy of which is attached as Appendix B and is fullyincorporated by reference herein.

Mobile Transceiver Operation

The operation of a mobile transceiver 12 within the distributive widearea network transmission trunked communication system of the presentinvention will now be described with reference to the flow diagramsdepicted in FIGS. 14-17.

FIG. 14, broadly depicts in flow diagram format, how a mobiletransceiver 10 communicates in the communications system of the presentinvention. The transceiver is powered up in the initialize radio step300. Operational flow is then immediately directed to the step 302wherein the transceiver 10 goes to its preassigned home channel.Operational flow then proceeds to step 304, where the transceiver 10listens for incoming signals transmitted on its home channel. Asdescribed in detail above, the transceiver will be monitoring its homechannel, or other temporarily assigned channel, for signallinginformation relating to system priority, channel availability, etc.,that is broadcast by the system.

Operational flow proceeds to step 306, to initiate a system transmissionrequest, when the operator of the transceiver desires to transmit. Therequest to communicate is acknowledged in step 308 through a returncontrol signal transmitted by the assigned repeater, and operationalflow proceeds to step 310 where the transmission takes place. Once thetransmission has been completed the transmitter is released in step 312,and operational flow returns to step 304 where the system continues tomonitor the system for activity.

The monitor system for activity step 304 of FIG. 14 is described ingreater detail in FIGS. 15a through 15c. Operational flow first proceedsto decision block 320 to determine whether the transceiver squelch hasbeen opened for the channel currently being monitored. If the squelch isnot open (i.e. the transceiver is not receiving any signals),operational flow is directed to decision block 322 to determine whetherthe squelch has been closed for a predetermined time frame (such as 20milliseconds). Operational flow is directed to step 324, where thechannel currently being monitored is marked as being free, if thesquelch has been closed for the predetermined time period. Operationalflow is then directed back to decision block 320 to again determinewhether the squelch has become open. If the squelch has not been closedfor the appropriate predetermined time, operational flow is directedfrom decision block 322 directly to block 320, without marking thechannel as free. Requiring the squelch to be closed for a predeterminedtime before marking a channel as free prevents false indications ofchannel status caused by spurious noise that may be received by thetransceiver.

Operational flow is directed from decision block 320 to step 326 if thesquelch is determined as being open (i.e. it is determined that thetransceiver is receiving signals). At step 326, the transceiver appliesthe system key, described herein above, and attempts to decode thecontrol message received by the transceiver. The transceiver willattempt to decode the control message for a predetermined time ofapproximately 250 milliseconds. Operational flow is then directed todecision block 328 to determine whether the control message 152 wasdecoded. If nothing was decoded, operational flow proceeds to step 329.At step 329 the transceiver determines if three consecutive attempts todecode the control-message 152 have been attempted. If there has notbeen three consecurive attempts then operational flow returns to step320 where the transceiver continues to monitor its assigned channel. Ifthere has been three consecutive attempts then operational flowcontinues to step 324 and the channel is marked as free.

Operational flow is directed from decision block 328 to decision block330, if it is determined that a proper control message has been decoded,where the transceiver will determine whether the incoming transmissionis addressed to it. If the incoming transmission is addressed to thetransceiver, operational flow proceeds to step 340 where the incomingsignal is received and processed.

Operational flow is directed from decision block 330 to step 332, if thereceived transmission is not addressed to the transceiver. The freechannel and system access priority information included in the receivedin the control message is at that point saved by the transceiver.Operational flow is then directed to decision block 334 where it isdetermined whether the push to talk switch of the transceiver isdepressed (indicating the operator of the transceiver desires to make atransmission) or not. If the push to talk switch is depressed,operational flow is directed to step 306 where the transceiver initiatesa system communication request. It will be appreciated that the freechannel and system access priority data saved in step 332 will be usedin the system communication request procedure.

Operational flow is returned from decision block 334 to step 320, if thepush to talk switch is not depressed, where the transceiver continues tomonitor for incoming transmission.

FIG. 15b depicts in detail the active receive information step 340 ofFIG. 15a. At step 342, in FIG. 15b, the control message received by thetransceiver is analyzed to determine which channel-the transceiver needsto change frequencies to receive the transmission intended for it, andthe transceiver is switched to that channel. Operational flow is nextdirected to decision block 344 where it is determined whether thetransceiver is being addressed as part of a "normal" group oftransceivers (i.e. a predetermined group of listeners such as a squad ofpolice cars, fleet of taxi cabs, etc.), or whether the transmissionbeing received by the transceiver is for a special group functions. Ifthe transmission being received by the transceiver is for a specialgroup function, operational flow proceeds to step 400 (detailed in FIG.15c).

Operational flow is directed from decision block 344 to decision block346 if the control message is addressed to a normal group of users.Decision block 346 determines whether the transceiver has been disabledor not. As described hereinabove, the transceiver can be remotelydisabled from either receiving or transmitting. For instance, if aparticular user is no longer an authorized user, the transceiver can beautomatically disabled. The position of decision block 346 in relationto the determination of whether the group ID is a "normal" group isimportant in that a special group function as detailed In FIG. 15c, canbe processed by the transceiver whether or not the transceiver has beendisabled for normal voice communications or not. If the transceiver hasbeen disabled, operational flow proceeds to step 304 for furthermonitoring of the system.

Operational flow proceeds from decision block 346 to step 348 if thetransmission received by the transceiver is for a normal group ID andthe transceiver has not been disabled. At step 348, the receive audio onthe transceiver is opened, portions of the control message are saved bythe transceiver for comparison in later steps, and a record entitled"data words try" (for reference later in the program at Step 364) is setto zero.

Operational flow proceeds from step 348 to decision block 350 where thetransceiver determines if the squelch continues to be open. If thesquelch has been closed, operational flow is directed to decision block352 to determine whether the squelch has been closed for a predeterminedtime (such as 250 millliseconds). If the squelch has not been closed forthe predetermined amount of time, operational flow returns from decisionblock 352 to decision block 350 to determine whether the squelch hasbeen opened in the interim. The 250 millisecond delay in operationalflow is used to prevent disconnection of the transceiver due tomomentary fades in the incoming signal, or similar short interruptionsof the signal. If the squelch has been closed for the predeterminedamount of time, operational flow proceeds to step 364.

Operational flow proceeds from decision block 350 to step 360 if thetransceiver squelch remains open. At step 360, the transceiver tries toagain decode the control message. This is a repeat of the decodefunction performed at step 326. The second decode operation is requiredto ensure that the transceiver remains on the assigned channel throughthe transmission. Operational flow proceeds from step 360 to decisionblock 362 to determine whether successful decoding of the controlmessage was accomplished. If there was not a successful decoding,operational flow is directed from decision block 362 to step 364 wherethe "data words try" record referred to in step 348 is incremented byone. Operational flow then proceeds to decision block 366 where it isdetermined whether there have been ten attempts to decode the controlmessage. If there have not been ten attempts to decode the controlmessage, operational flow is returned from decision block 366 todecision block 350 where, if the squelch still remains open, anotherattempt at decoding the control message is made. If ten unsuccessfultries at decoding the control message are made, operational flow isdirected from decision block 366 to steps 354 and 356 where the receiveaudio is closed, the transceiver is directed back to its home channel,and operational flow again returns to the monitor system activity step304.

Once the control message has been successfully decoded, operational flowproceeds from decision block 362 to decision block 370, where thecontrol message decoded in step 360 is compared to the control messagesaved in step 344. The comparison is required because control messagesare continuously transmitted by the system, and it is possible that therepeater could interleave different control signals on the same channelduring the time the transceiver is receiving a transmission. Comparingthe control signals received during a transmission to the control signalthat initiated reception of the transmission is required so that thetransceiver will not shift to receive a second transmission having adifferent control signal. If the control message is the same as thesaved control message, and if the "go to" field of the control messageis the turn off code (indicating the end of the received transmission),operational flow is directed to steps 354 and 356 where the receiveaudio is closed, the transceiver is set to the home channel, and iscleared of any auxiliary and telephone settings. Operational flow thenproceeds to step 304 for continued monitoring of system activity.

Operation flow is directed to decision block 372 if the tests of block370 are not both met. Operational flow is directed from decision block372 to step 374 if the control message decoded at step 360 is the sameas the control message saved in step 348, and the "go to" field is ahang code. The receive audito is closed in step 374 and operational flowis returned to step 304 for continued monitoring of system activity. Itwill be noted that the operation flow does not reset the transceiver tothe home channel when the long code is detected. The option to "hang"the transceiver on a channel, while closing the receive audio, can beused to hold the channel to maintain the priority of an individual call.

Operational flow is directed to decision block 376 if the tests of block372 are not met. If the control message decoded in step 360 is the sameas the message saved in step 348, operational flow is redirected to step342. It will be appreciated that operational flow will stay in a loop tostep 392 throughout a received transmission as long as the receivedcontrol message remains unchanged.

Operational flow is directed to decision block 378 if the test of block376 is not met. The transceiver can be preprogrammed with two separategroup IDs. If the group ID of the control message decoded in step 360 isone of the two preprogrammed group IDs, operational flow is directedfrom block 378 to step 342. If the test of block 378 is not met,operational flow is directed to step 364.

The processing of special group IDs, step 400, is depicted in detail inFIG. 15c. Operational flow is first directed to decision block 402 whereit is determined whether the special group ID is an "all call" ID (i.e.,all transceivers are to receive the communication). If the special groupID is an "all call" ID, operational flow is directed back to decisionblock 346 of figure 15b. If the transceiver has not been disabled(decision block 346), the incoming transmission is processed forreception by the transceiver as described above.

Operational flow is directed from decision block 402 to decision block404 if a special group ID is not an "all call" ID. Block 404 determineswhether or not there is an "interrogate" special group ID presented bythe control message. The interrogate function instructs the transceiverto immediately respond to the transmitting repeater with the presentstatus of the transceiver. In particular, the operator of thetransceiver can selectively input a message to be automaticallytransmitted to the repeater as to what the operator is presently doing(for example, the operator is not in the vehicle, the operator hascompleted an assigned job, or the operator is waiting for a newassignment). Operational flow is directed to the decision block 406 ifthe test of block 404 is met. At block 406, it is determined whether thetransceiver has been disabled from the interrogate function. Forinstance, if the transceiver had been stolen, and the system no longerwishes to track the location of the mobile, the interrogate function ofthe transceiver could be disabled. If the transceiver has not beendisabled from the interrogate function, operation flow proceeds fromdecision block 406 to step 408 where the preprogrammed response to theinterrogate special group ID is transmitted.

Operational flow is directed from decision block 404 to decision block412 if the group ID is not an "interrogate" signal for the transceiver.Operational flow is then directed from decision block 412 to step 410 ifthe transceiver has been disabled. The transceiver is set to its "home"channel at step 410 and is directed back to step 304 for continuedmonitoring of system activity.

Operational flow is directed from decision block 412 to decision block414, where it is determined whether the special group ID is an auxiliarycall for the transceiver, if the transceiver has not been disabled. Ifthe incoming transmission is an auxiliary call, (i.e., an individual asopposed to a fleet call to a particular transceiver), operational flowis directed from decision block 414 to step 416 where the incoming callis marked for full duplex communications to handle the auxilliary call.Operational flow is then directed from step 416 to decision block 346 ofFIG. 15b.

Operational flow is directed from decision block 414 to decision block418 if it is determined that the incoming transmission is not anauxiliary call for the transceiver. At decision block 418 it isdetermined whether the incoming transmission is a telephone call for thetransceiver. If the incoming transmission is a telephone call for thetransceiver, operational flow is directed from decision block 418 tostep 420 where the incoming transmission is marked for full duplexcommunications to handle the telphone call. Operational flow is thendirected from step 420 to decision block 346 of FIG. 15b.

Operational flow is directed to decision block 422 if the test of block418 is not met. At block 422 it is determined whether the incomingtransmission is a dynamic reassignment for the transceiver. If theincoming transmission is a dynamic reassignment for the transceiver,operational flow is directed to step 424 where the dynamic reassignmentoccurs, as described hereinabove. Operational flow is then directed fromstep 424 to step 410 and is then returned to step 304 for continuedmonitoring of the system activity.

Operational flow is directed from decision block 422 to decision block426 if the incoming transmission is not a dynamic reassignment for thetransceiver. At decision block 426, it is determined whether theincoming transmission is a disablement command for the transceiver. Ifthe incoming transmission is a disablement command, operational flow isdirected to step 428 where the transceiver is disabled. Operational flowthen proceeds to step 410 for reassignment of the transceiver to itshome channel, and then to step 304 for continued monitoring of thesystem.

The initiate system communication request step 306 is depicted in detailin FIGS. 16a and 16b. Operational flow is first directed to decisionblock 450 where it is determined whether the push to talk switch hasbeen depressed by the operator of the transceiver. If the push to talkswitch has not been depressed, operational flow is directed to step 452where the transmitter is unkeyed, and operational flow is returned tostep 304 for continued monitoring of the system activity. Operationalflow is directed from decision block 450 to decision block 454 if thepush to talk switch of the transceiver is depressed by the operator. Atdecision block 454, it is determined whether the radio has beendisabled. If the radio has been disabled, operational flow proceeds fromdecision block 454 to decision block 460 where it is determined whetherthe push to talk is still depressed. If the push to talk switch is stilldepressed, and the radio has been disabled, operation flow remains atblock 460. Once the operator releases the push to talk switchoperational flow is directed to step 462 where the busy tone andintercept tone is released and the operational flow is directed to step304 for continued monitoring of the system activity.

Operational flow is directed from decision block 454 to decision block456 if the push to talk switch is depressed and the transceiver has notbeen disabled. The priority of the desired outgoing transmission iscompared to the current system access priority. It will be appreciatedthat the determination of access priority is being made at thetransceiver, prior to any outgoing transmission being made by thetransceiver. If the transmission priority in the transceiver is notequal to or higher than the current system access priority, operationalflow is directed to step 458 where the busy tone is initiated.

Operational flow is directed from decision block 456 to decision block470 if the priority of the desired outgoing transmission is equal to orhigher than the current system access priority. At decision block 470,it is determined whether an auxiliary or telephone group has beenreceived. If the auxiliary or telephone group has been received,operational flow is directed from decision block 470 to step 500 forcommunication request acknowledgement, since the handshakingrequirements of steps 472-492, and 460, 462 are not required in fullduplex operation of the transceiver.

It will be appreciated by those skilled in the art, that if full duplexoperation is not provided for, a handshaking procedure must be followedto initiate communications. The handshaking procedure is initiated bydirecting operational flow from decision block 470 to step 472 where thetransceiver is directed to a free channel. Operational flow nextproceeds to step 474 where one control message is transmitted from thetransceiver to the repeater initiating the call. Also in step 474, therecord of the number of attempts made by the transceiver to transmit acontrol message to a repeater is incremented by one. It will beappreciated that the record of transmitting attempts ("TXAMPTS") iszeroed out at step 306 where the system communication request isinitiated.

Operational flow is next directed to step 476 where the transceiverattempts to obtain a control message back from the repeater in responseto the transmission at step 474. The attempt at step 476 continues forapproximately 250 milliseconds. Operational flow is next directed todecision block 478 where it is determined whether or not a controlmessage was received and decoded by the transceiver. If a controlmessage was decoded, operational flow proceeds to decision block 484where it is determined whether or not the received control message wasin fact a response to the request initiated at step 474. Assuming thereponse was valid, operational flow is directed from block 484 to step500 where the communication request is acknowledged and fullcommunication is allowed.

If no control message is decoded at decision block 478, operational flowis directed to block 480 where it is determined how many attempts attransmitting a control message from the transceiver (step 474) have beenmade. If a predetermined number of attempts (for instance 10) have notbeen made, operational flow is redirected to decision block 456 to setup another attempt at establishing a handshake between the transceiverand the repeater. If more than 10 attempts have been made, operationalflow is directed to step 482 where an intercept tone is presented by thetransceiver to the operator, indicating that the handshake was notaccomplished, and communications have not been established. Operationalflow then proceeds from step 482 to decision block 460 where it isdetermined whether the push to talk switch has been depressed. If thepush to talk switch is depressed operational flow is hung at decisionblock 460 until the push to talk swtich is released. Once the push totalk switch is released, operational flow proceeds from decision block460 to step 462 where the intercept tone and the busy tone are turnedoff. Operational flow then returns to step 304 for continued monitoringof system activity.

Returning to decision block 484, if a control message is received by thetransceiver, but the control message received is not a proper responseto the handshake, operational flow is directed to decision block 486. Itwill be appreciated that receiving any response to the handshake, evenif not a proper response, is preferable to receiving no response,because it indicates to the transceiver that it is in communicationsrange. At decision block 486, the transceiver determines whether thecontrol message received indicates that the same channel is alreadyoccupied. Operational flow is directed to step 488, if the channel is sooccupied, where the free channel information and system access priorityinformation is saved from the received control message. Operational flowis then redirected to step 450 where the handshaking procedure willagain be initiated.

Operational flow is directed to decision block 490 if the test of block486 is not met. Operational flow will be directed from block 490 to step492 and then back to step 476 if there have been less than twoconsecutive trys to decode a control message received in response to thecontrol message transmitted at step 74 by a transceiver. If there havebeen two consecutive attempts at decoding, operational flow is returnedto block 450 where another attempt at handshaking will be made.

The communication request is acknowledged at step 500, when a successfulhandshake is made. Operational flow is then directed to block 502.Decision block 502 is a user selectable feature. A proceed tone can beenabled if the user of a transceiver wants to hear an audible signalwhen a communication request has been acknowledged. If the proceed tonefeature is enabled, operational How proceeds from its decision block 502to step 504 where the audible tone is initiated, and is then directed tostep 506. If the proceed tone feature is not enabled, operational flowproceeds directly from decision block 502 to step 506 and thetransceiver control message and voice circuits are enabled.

Operational flow proceeds from step 506 to decision block 508 where itis determined whether the push to talk switch is active. The operationalflow will stay at step 508 as long as the push to talk switch isdepressed, or until a predetermined time out period expires. Once thepush to talk switch is released, operational flow proceeds to step 512where the voice circuit is disabled, and then to step 514 where onecontrol message with a turnoff code is transmitted. Operational flowthen proceeds to decision block 516 to determine whether the transceiverhas been set for full duplex opertion. The transceiver is maintained atthe channel it is currently on (step 518) if communications are fullduplex. The transceiver is reset to its home channel (step 520), if fullduplex operations are not required.

We claim:
 1. A remote network switch for a land mobile transmissiontrunked communication system, the land mobile transmission trunkedcommunication system having a plurality of transceiver means fortransmitting and receiving radio communications over one or more radiochannels, the remote network switch comprising:a plurality of repeatersites, each repeater site comprising a plurality of repeater means, eachrepeater means for establishing transmission trunked radiocommunications on a preassigned one of the radio channels between therepeater means and one or more transceiver means, the transmissiontrunked communications having either voice information, datainformation, or both, and a control signal, and the plurality ofrepeater means at a repeater site operably connected together by a highspeed bus means for synchronously communicating control signals amongthe plurality of repeater means using a variable time multiplex systemhaving a frame time period which is based on a number of repeater meansat the repeater site; and switch means for selectively interconnectingtwo or more repeater means at two or more repeater sites in response toa control signal from a transceiver means, the switch means operablyconnected to each of the repeater means by a network bus means separatefrom the high speed bus means, for synchronously communicating controland information signals between the repeater means and the switch means.2. The remote network switch of claim 1 wherein each of the transceivermeans is assigned a unique identification number that is communicated aspart of the control signals.
 3. The remote network switch of claim 1wherein the information signals for the transmission trunked radiocommunication are transmitted on a distributively selected one of thepreassigned radio channels for the repeater means and the controlsignals for the transmission trunked radio communications aretransmitted simultaneously in the subaudio range of the same channelover which the information signals are transmitted according to apredetermined control signal format.
 4. The remote network switch ofclaim 1 wherein the predetermined control signal format comprises:afirst predetermined control signal format when the control signals aretransmitted from the transceiver means to the repeater means having:anine bit Sync field that initializes and synchronizes the repeatermeans; a one bit Reserved field that indicates a transceiver meanscontrol message; a ten bit GoTo field that contains a directly decodablepredetermined radio channel number of one of the repeater mans to whichthe control signals are being transmitted; a five bit Home field thatcontains a predetermined home number of the transceiver means sendingthe control signal; an eight bit Group field that contains a Group IDcode of a fleet or subfleet of transceiver means which are being called;a three bit Status field that defines the status of the transceivermeans; a thirteen bit Unique ID field that contains the uniqueidentification number for the transceiver means; a three bit Priorityfield that indicates a predetermined priority level assigned to thetransceiver means; and an eight bit Checksum filed that includes a sevenbit truncated BCH encoding scheme checksum and a single bit parity; anda second predetermined control signal format when the control signalsare transmitted from the repeater means to the transceiver meanshaving:a nine bit Sync field that initializes and synchronizes thetransceiver means; a one bit Reserved field that indicates a repeatermeans control message; a ten bit GoTo field that contains a directlydecodable predetermined radio channel number of one of the repeatermeans that the transceiver means should tune to in order to receive thecontrol signals that are being transmitted by that repeater means; afive bit Home field that contains a predetermined home number of one ofthe repeater means; an eight bit Group field that contains a Group IDcode of a fleet or subfleet of transceiver means which are being called;a ten bit Free field that contains a directly decodable predeterminedradio channel number of one of the repeater means that is not busy andis available for service; a thirteen bit Unique ID field that containsthe unique identification number for the transceiver means; a three bitPriority field that indicates a current operating priority level for allof the repeater means; and an eight bit Checksum field that includes aseven bit truncated BCH encoding scheme checksum and a single bitparity.
 5. The remote network switch of claim 4 wherein the first andsecond predetermined control signal formats are further encrypted usinga two word encoding key to encode and decode each control signaltransmission whereby a first word encoding key is used to encrypt theentire first or second predetermined control signal except the Syncfield and a second word encoding key is used to encrypt the Checksumfield.
 6. The remote network switch of claim 1 wherein the controlsignals are communicated among the repeater means by the high speed busmeans according to a first bus protocol and wherein the control signalsand the information signals are communicated between the repeater meansand the switch means by the network bus means according to a second busprotocol.
 7. The remote network switch of claim 1 wherein the first busprotocol is arranged into a plurality of messages, one message for eachof the repeater means, each message having a predetermined number ofwords that are made up of a predetermined number of bits, and whereinthe first bit of each word is a sync bit and only the first bit of thefirst word of a message is set to one to indicate the start of a newmessage and the first bit of all other words of the message are set tozero.
 8. The remote network switch of claim 7 wherein each of therepeater means detects the sync bit for each message and if the sync bitis not present, updates a count of a number for the repeater means andchecks for the sync bit of the next message from the next repeater meanswhereby the total time to transmit the messages according to the firstbus protocol can be less than the total number of messages if one ormore repeater means does not transmit a corresponding message.
 9. Theremote network switch of claim 1 wherein any of repeater means may beadded to or removed from the high speed bus means without affecting theoperation of the remote network switch and wherein no one of therepeater means is responsible for synchronization of the high speed busmeans.